As a physiotherapist, I find myself constantly learning from my clientele. Most recently I have learned of the phenomenon "Runner's gut". This where runners suffer from a range of digestive symptoms of nausea, vomiting, and/or diarrhea.
I came across an interesting article on the matter worth considering if you display abdominal discomfort during or after running:
http://www.washingtonian.com/blogs/wellbeing/fitness/8-tips-for-avoiding-runners-stomach.php
In one client, manual treatment of the mesenteric root proved effective in alleviating these symptoms, quite interesting!
http://www.anatomyexpert.com/structure_detail/4820/1337/